From U.S. Pat. No. 4,637,402, it is known to measure the hearing deficit of a person and to fit a hearing aid to said person. Frequency bands are determined over which said person's hearing level is unacceptable, and these bands are then shifted—in a harmonic-sustaining manner—to bands with an acceptable hearing level. Said frequency bands are determined by means of a swept frequency tone generator. Furthermore, after initial values are chosen for the various gains and gainshaping elements, said person is then presented with well known word discrimination lists, i.e. spoken words which are known to differ in subtle ways from other words, and his test scores are taken. On the basis of the types of words that are missed and the spectral content of those words, the appropriate gain changes, and if necessary transposition placements and characters are altered. I.e., a recognition test is carried out, and dependent on the result of that recognition test, parameters related to the frequency transposition are altered.
In U.S. Pat. No. 6,212,496, a technique for producing an audio output customized to a listener's hearing impairment through a digital telephone is disclosed. By determining hearing thresholds for many frequencies, unacceptable regions (frequency ranges) are determined, in particular frequency bands in which the user cannot hear. The unacceptable band or bands is/are then mapped onto one or more acceptable bands.
It is desirable to provide an alternative way of adjusting parameters related to frequency transposition in a hearing system, and to provide a arrangement for carrying out such adjustments.
In WO 2004/054318 A1, a method for fitting a portable hearing device to a hearing-impaired user is disclosed. The method shall lead to well-adjusted frequency-dependent gain curves and comprises a consonant discrimination step, in which an A-B-discrimination test with the sound of the letter “s” present or absent is carried out. If the user can hear the difference, high frequencies are left unchanged; if the user cannot hear the difference, high frequencies are boosted. There is no mention of frequency transposition.
From EP 1 441 562 A2, hearing devices are known, in which frequency transposition is implemented. Methods for carrying out frequency transposition, in particular frequency compression, are therein disclosed in detail.
In B. C. J. Moore “A test for the diagnosis of dead regions in the cochlea”, British Journal of Audiology Vol. 34, No. 4, 2000, pages 205-224, a procedure for measuring psychophysical tuning curves (PTCs) is disclosed. Said procedure comprises, for several test frequencies, determining the threshold of perception of a sinusoid of said test frequency in presence of a masker, wherein a noise band was used as the masker.